Tramming a Vice for CNC

[awemawson]

I've recently made some stepped jaws for my Sagop CNC vice on my Beaver Partsmaster to hold a part I'm making a few of. Re-mounting the vice of course it needed tramming so I got to thinking just how close to square can I get.

Simply squaring the long axis of the vice with an accurate long set square to the machine table got me to 14 microns across the 125 mm width of the jaws - so about 1/2 a thou in 5 inches - much better than I'd expected.

Using John Stevenson's cunning method of gripping an accurate piece of plate shaped like an inverted 'U' in the jaws so the legs project into the tee slots and snugging the legs to the slot got me to the same 14 microns.

Gentle tapping with the soft hammer can get me to maybe 2 or 3 microns before I start going round in circles. (By the way I'm measuring using the Heidenhain touch probe controlled by the TNC355 to remove the 'human' factor)

Now of course as I'm machining the rebates for these jaws on the machine itself any errors will be milled away so all this anal fussing is irrelevant, but this was just an exercise in 'can I'.

So how close do you reckon to set your vice and what tricks do you use to achieve this accuracy?

(BTW stepped jaws not fitted in the photo and vice is at 90 degrees to where I was tramming it)

Andrew

[TomG]

I'm not nearly anal enough to be posting here, but you did ask.

The following technique works amazingly well and takes very little time.

Tom

[awemawson]

Yes Tom I've seen your video and used that technique on my manual mill.

But what I'm saying is what is your residual error - it isn't zero, there must be a finite error. I expect that you are using a 'tenths' indicator there but I don't think you say (unless I missed it) - so assuming you are at the 'tenths' level we are talking 2.5 microns or roughly where I am.

Andrew